Hearing aid



FIG. 1 is a front perspective view of the hearing aid;

FIG. 2 is a front view thereof;

FIG. 3 is a left side view thereof; and,

FIG. 4 is a rear view thereof.

The broken lines illustrate portions of the hearing aid that form no part of the claimed design; the broken lines form no part of the claimed design. 

CLAIM The ornamental design for a hearing aid, as shown and described. 